The Top Contributing Causes of Hypothyroidism

Underactive Thyroid

Hypothyroidism, or underactive thyroid, is a common condition in which your thyroid gland doesn't produce enough thyroid hormone. This essential hormone is necessary to regulate many of your body's daily functions, and having too little can lead to a variety of symptoms. "This hormonal imbalance can cause weight gain or make it difficult to lose weight, even with vigorous exercise and the right diet," says Scott Isaacs, MD, medical director at Atlanta Endocrine Associates and author of Hormonal Balance: How to Lose Weight by Understanding Your Hormones and Metabolism. According to estimates, about 4.6 percent of the U.S. population over age 12 has hypothyroidism. What's more, the National Thyroid Institute estimates that millions of Americans are living with undiagnosed hypothyroidism. Although it can't be fully prevented, there are multiple factors that can contribute to developing the condition.

Hashimoto's Thyroiditis

According to Dr. Isaacs, a condition called Hashimoto's thyroiditis, or chronic lymphocytic thyroiditis, is the top cause of hypothyroidism that eventually leads to treatment, and it's estimated to affect 15 to 20 million people in the United States. "Hashimoto's thyroiditis may begin as a short period of thyroid overactivity, triggered because the gland is being destroyed by the immune system," he explains. "It's hereditary and affects women seven times more often than it does men. It's frequently triggered by a stressful event." Hashimoto's is often distinguished by a goiter, a swelling of the thyroid gland, which causes a lump at the base of the neck. Research published in the journal Thyroid found that the condition is tied to hypothyroidism symptoms such as fatigue, irritability, and nervousness, as well as cancer risks.

Causes of Hypothyroidism

The prescription drug lithium, sometimes used to treat mania in bipolar disorder, is a well-known cause of hypothyroidism, but there are other medications that can lead to symptoms as well. Epilepsy drugs, drugs that contain iodine, chemotherapy drugs, and drugs used to fight infection are considered potential causes of hypothyroidism, Isaacs says. Still, lithium's role remains the strongest. In a recent study of more than 160 elderly people, the rate of hypothyroidism was 35.4 percent among people on lithium, compared to 7.1 percent in those who don't take it.

Pregnancy

Pregnancy isn't a cause of hypothyroidism, but an underactive thyroid can have serious consequences during pregnancy, especially if it hasn't been diagnosed. "Hypothyroidism in pregnancy is a serious issue," says Isaacs. "It's estimated that 2.5 percent of pregnant women have some form of hypothyroidism; however, the symptoms may overlap those of being pregnant and the diagnosis may be missed." Possible consequences of hypothyroidism during pregnancy include an increased risk for complications such as miscarriage and developmental and intelligence defects in the baby. If you're pregnant and have hypothyroidism, you should have your levels tested every four weeks, Issacs advises. That's a precaution that's not always followed, though — a European study found that practices for screening for hypothyroidism during pregnancy varied widely.

Treatment for Hyperthyroidism

The opposite of hypothyroidism is a condition called hyperthyroidism, in which your body produces too much thyroid hormone. And hyperthyroidism treatment can actually be a cause of hypothyroidism symptoms. "Hypothyroidism is a frequent outcome of radioactive iodine treatment for hyperthyroidism or thyroid cancer," Isaacs explains. "Thyroid formulas that contain iodine are intended to boost thyroid function, but may interfere with its function." Despite this risk, a British study published in the journal Endocrine Abstracts found that inducing hypothyroidism is preferable to hyperthyroidism in many cases, and can actually improve your chances of survival from severe hyperthyroidism.

Thyroid Surgery

Thyroid surgery, or thyroidectomy, to remove part of the thyroid is a treatment for hyperthyroidism, and one that also reduces thyroid function and becomes a cause of hypothyroidism. "Thyroid surgery is used as a last resort," says Eva Cwynar, MD, an endocrinologist and author of The Fatigue Solution: Increase Your Energy in Eight Easy Steps. "It's most used during pregnancy because pregnant women can't be given radioactive iodine, and many prefer not to use medications that slow down the thyroid because of the potential side effect on the fetus." On a positive note, having thyroid surgery doesn't automatically mean you'll develop hypothyroidism. A study in the Annals of Surgery of almost 300 people who underwent partial thyroid surgery found a hypothyroidism rate of less than 11 percent.

Iodine Deficiency

A deficiency of the needed mineral iodine is another cause of hypothyroidism symptoms. Dr. Cwynar notes that iodine deficiency is the number one cause of hypothyroidism worldwide. "In more recent years, it's affected millions of Americans," she says. "This relates back to the U.S. Food and Drug Administration deregulating iodine in salt preparations. Look at your salt label and make sure there's a substantial amount of iodine in it."

Getting Tested for Hypothyroidism

Although there are numerous causes of hypothyroidism, there's one simple way to detect it, and that's with a blood test. "Thyroid experts recognize the thyroid stimulating hormone (TSH) test as the test of choice when a doctor suspects thyroid dysfunction," Isaacs says. "An elevated TSH test accurately diagnoses hypothyroidism 80 percent to 90 percent of the time." Since other conditions such as rheumatoid arthritis and fibromyalgia can mimic the symptoms of hypothyroidism, it's important to work with your doctor to get an accurate diagnosis. Once you are diagnosed, hypothyroidism treatment is simple and effective.

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